1. Field of the Invention
The present invention relates to an audio data transmission apparatus and method for transmitting, over audio data, additional information such as a copy inhibit control signal and an author right information for tracing an unauthorized copy; an audio data recording apparatus for recording the audio data which has been received; and an audio data recording medium containing the additional information overwritten on the audio data.
2. Description of the Prior Art
Recently, the use of digital audio apparatuses such as a compact disc (CD) player and a so-called mini disc (MD) using a small-size optical disc has become widespread, enabling users to easily reproduce an audio signal of a high quality.
On the other hand, however, a lot of music software may be copied without a limit and various copy prevention methods have been suggested.
Especially in the case of the aforementioned digital audio, the audio signal is not deteriorated through copying, which makes copy prevention very important. In the case of the aforementioned digital audio, a copy inhibit control signal consisting of a copy inhibit symbol or a copy generation limit symbol as well as an author right data are additionally recorded in additional to a digital audio signal on a recording medium, so as to prevent copying or to trace a recording medium copied using an authorized data.
However, when a digital audio signal is converted into an analog audio signal, the aforementioned additional digital data is not contained in the analog audio signal, making it impossible to prevent illegal copying or trace unauthorized copying.
To cope with this, it is desired to overlap the aforementioned additional information in an analog audio signal. However, it has been quite difficult to overlap an additional information on an analog audio signal without deteriorating the audio signal S/N ratio, although such a technique of overlapping an additional information is expected to enable a novel service in the information-oriented society.
To cope with this, a spectrum diffusion method is considered for overlapping an additional information. This method is preferable for overlapping a plenty of data, but when used for an audio signal, it is impossible to obtain a sufficient band width and it has been difficult to realize in the field of music source and the like which requires to maintain a high S/N ration.
Moreover, in order to carry out spectrum diffusion on an audio signal, there arises a problem of synchronization. Firstly, in an audio signal, it is necessary to provide a significantly long periodicity so as to obtain a sufficient S/N ratio, and a long time is required if an ordinary serial search is used for synchronization establishment.
In contrast, a method called matched filter is known for improving the synchronization establishment in a dedicated circuit. However, when the periodicity is so long, the circuit size becomes great and it is not practical in costs to mount such a circuit in a reproduction apparatus and a reception apparatus. In a case when a decoder is mounted on an audio reproduction apparatus for carrying out a copy management from an analog audio input, a method desired is one which is easily available at a low price and can be used in common for various apparatuses. Because of these problems, it has been considered difficult to realize a data multiplexing using the spectrum diffusion method.
It is therefore an object of the present invention to provide an audio data transmission apparatus and method, an audio data recording apparatus, and an audio data recording medium which are capable of multiplexing spectrum-diffused data on an analog audio signal with minimum deterioration of the audio quality.
The audio data transmission apparatus according to the present invention includes gap insert position detecting means and gap insert means, so that gaps is inserted by the gap inserting means at a position detected by the gap insert position detecting means. This gap is used as a control signal for multiplexing on the audio signal a spectrum-diffused data obtained according to an additional information.
Moreover, the audio data recording apparatus according to the present invention uses as a control signal the gap from the gap detection means, so that a demodulation means demodulates a spectrum-diffused data multiplexed on an audio signal, and according to the demodulated additional information, correction means corrects the spectrum-diffused data.
Moreover, the audio data recording medium according to the present invention contains an additional information as a spectrum-diffused data which is multiplexed on an audio signal using a gap as a control signal.